Currently you need to write a process that removes the old files. This can be done either through DTS or a T-SQL script.
One thing you could do is read the backup history files and then delete older files for that database using xp_cmdshell.
The next major release of SQL LiteSpeed will have a GUI front-end as well as a process to convert existing Maintenance Plans to use SQL LiteSpeed.
If you are interested in scripts for SQL LiteSpeed you can contact Craig Allen email@example.com at Edgewood Solutions. He has some scripts that have been submitted by other clients.